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WORLD PULPPAPER 57 High hygiene can only be achieved through very close cooperation between the biocide supplier and the mills production personnel specifications. Beside the scientific facts which we have discovered we have also concluded that high hygiene can only be achieved through very close cooperation between the biocide supplier and the mills production personnel. HYGIENE CONTROL IS ALL ABOUT SPORE CONTROL Depending on end uses board machines have various hygiene targets for food packaging. Many specifications are based on a maximum acceptable level of aerobic bacteria in the final dry board. For example LPB for milk products normally must contain less than 250 CFU of living aerobic bacteria per gram in dry board. In reality however we have found the quantity of aerobic bacteria in the final dry board depends on bacterial spores only. These spores are thermo-tolerant forms of bacteria sleeping cells and when they are mature they can survive the heat of the dryer section whereas vegetative growing bacteria cells and incomplete spores are destroyed by heat. Therefore spores are the real bad guys regarding food board hygiene. Figure 1 gives additional examples of this. Figure 1a shows a scanning electron microscope picture of cells of non- spore forming paper machine bacteria Deinococcus geothermalis growing on stainless steel surface. Figure 1b shows vegetative cells of Rubellimicrobium bacteria in process water. None of these vegetative cells can endanger hygiene of final board as they are effectively killed by the heat of the drier section. Figure 1c shows a transmission electron microscope picture of a mature spore just being released from a Bacillus cell. If present in wet paper web these thermo- tolerant spores will survive through the heat of the dryer section and are alive in the dry finished board. Hygiene control is all about spore control. TROUBLE ON THE MACHINE DESPITE HIGH BIOCIDE LEVELS In our work with hygiene in mills we have observed several food-packaging board machines that were running significant amounts of biocides but were still having difficulties in meeting strict end-product hygienic specifications. So despite intense use of biocides these machines were still periodically suffering from bursts of elevated levels of bacterial spores thus endangering the hygiene of the food-packaging board. Adding to the mystery some machines can run every day with high amounts of vegetative bacteria in process water and still not experience hygiene issues in board. In deeper studies on one board machine for example we observed an interesting phenomenon. In one process tank the total quantity of vegetative bacterial cells remained at essentially the exact same level for three consecutive days. However on day 1 the amount of spores was below detection limits on day 2 they jumped to very high levels and then on day 3 they were again below detection limits. Thus the vegetative cells were at stable levels but the spores were fluctuating from day to day. RD ON SPORE CONTROL Our RD programs aimed at reducing contamination in food-board mills have given us unique insight into the mechanism of sporulation what triggers it and what controls it in the board making process. This learning and new understanding in turn has supported the successful application of biocide solutions on hygienic board Bacillus Brevibacillus and Paenibacillus Among all aerobic bacteria that are capable of growing in the process of a board machine only these three genera are aerobic spore-formers A spore is inactive resting thermo-tolerant form of bacteria that resists the dryer heat Similar to other bacteria these prefer to grow multiply by simple cell division they make spores only if needed One cell produces only one spore of a threat to survival Killing of a mature spore requires a huge amount of biocide not economically affordable Prevention is the best approach stop bacteria from making a spore